1. Technical Field
The disclosed embodiments relate generally to shipping or transportation containers, specifically containers with a gas permeable membrane for the transport of products and commodities over long distances.
2. Description of Related Art
The use of shipping or transportation containers is known for the transport of products and commodities over long distances. To extend or otherwise preserve the shelf life of such transportable products the shipping containers are normally equipped with some form of temperature regulation system, such as a refrigeration system.
The combined proportions of carbon dioxide and oxygen in ambient atmospheric air are about 21%. However, such a ratio or composition of carbon dioxide and oxygen often does not suit or provide an optimal environment for enhancing the shelf life for many stored products.
Where the products to be transported are perishable goods, such as fruit and/or vegetables, transport containers may also incorporate a system adapted to modify the composition of the refrigerated air surrounding the stored contents. As fresh fruit and vegetables represent active biological systems the atmosphere of a container will constantly change as gases and moisture are consumed or produced by the metabolic processes (such as respiration) occurring within the biological systems present. Furthermore, the shelf life of a lot of shipped produce is highly dependent on the composition of gases within a container where the optimal gaseous composition of a storage container is highly dependent on the specific produce being stored.
When packed, fruits produce CO2 by using O2 that is present in the package due to respiration. To prevent decay of the fruits, it is required to control the CO2 level, e.g., by controlling the exposure of a permeable package wall (=membrane) towards the atmosphere, which contains hardly any CO2.
The basic idea behind this is that, due to the concentration gradient, CO2 will permeate through a permeable wall towards the air-side, thus lowering the CO2 level. In such systems, membranes having a high CO2 flux are desired.
By incorporating an atmospheric modification or control system into a transport container the respiration rates of the stored produce and the composition of gases present within a container may be regulated, thereby providing an effective means for prolonging the shelf life of the container contents in addition to the refrigeration of the air. In particular, the respiration rates of stored produce may be retarded by controlling the mix and/or partial volumes of oxygen, carbon dioxide and nitrogen within the container.
Because an opposite concentration gradient for O2 exists, O2 will permeate from the air side to the fruit side. To minimise this and thus prevent further production of CO2, membranes having a high CO2 flux and a high CO2/O2 selectivity are often used.
A common approach used in shipping containers to increase the shelf life of produce stored is to create an “ideal” or optimum storage atmosphere (that is different from that of ambient air) at the beginning of the storage period and to maintain that atmosphere. In some cases containers are initially flushed to remove or add gases resulting in an internal gas composition around the stored produce that is different from that of ambient air.
Once the oxygen content of the gases within a container drops further as a result of respiration, inlets may be opened to allow fresh air into the container, thereby delivering oxygen into the container. Such systems often rely on the use of membranes or films which are adapted to prevent the movement of gases into or out of the container, and such systems are commonly referred to as Modified Atmosphere (MA) systems.
However, by ventilating the container with fresh air and letting out the container air, the composition of the gas in the container will over time eventually result in a gas composition in which the carbon dioxide and oxygen content (as a sum proportion of container gases) approaches approximately 21%. Such a proportion of carbon dioxide and oxygen is not necessarily an optimal environment for the storage of certain products. If the container is not initially flushed, the sum of oxygen and carbon dioxide will always remain approximately 21%.
Although such systems may be relatively inexpensive to integrate into a container they are not well suited to adequately control and maintain optimum levels of carbon dioxide within a container, where such optimum levels often differ from those levels of carbon dioxide present in ambient air.
Moreover, the sum proportion of carbon dioxide and oxygen in a container will always remain approximately 21% unless the composition of either the outgoing and/or ingoing air is actively and effectively manipulated to thereby change this sum proportion (of 21%) as necessary. Other methods, for example the use of carbon dioxide absorbent lime, can be used to actively and selectively remove gases from the cargo space of a container. However, such methods have disadvantages including the disposal of used lime and ineffective control.
An alternative approach is to provide a container having concentrations of oxygen and/or carbon dioxide that are different from that of ambient air and regularly measuring and actively maintaining those concentrations during a storage period. In particular, such systems will typically maintain low levels of oxygen and higher levels of carbon dioxide (compared to ambient air) so that the levels of respiration occurring within stored produce may be controlled. To effectively gauge the concentrations and/or volumes of oxygen and other gases within a container such a system may often utilize sensor technology which is located within a container and is adapted to actively assess the gaseous composition inside the container. These systems are commonly referred to as Controlled Atmosphere (CA) systems.
Such Controlled Atmosphere (CA) systems are adapted to ensure that the appropriate remedial action is taken to ensure that the gaseous composition of a container is maintained, or returned to an optimal level when deviation occurs. To ensure optimal levels of gases are maintained (usually this involves reduced oxygen levels and increased carbon dioxide levels) many Controlled Atmosphere (CA) systems are provided with a filter adapted to compress and separate the components of incoming air. In this way, as air is directed into a container, excess oxygen may be prevented from entering the container, which is desirable as it will ensure the retardation of respiratory activity within the container.
Use of Controlled Atmosphere (CA) systems will enable a container to maintain the optimal gas composition specifically suited to the produce and/or goods contained within where such a gas composition may be actively controlled throughout the period of storage.
Whilst such a system may effectively control and maintain optimal conditions that will contribute to longevity of stored produce such systems are extremely expensive to manufacture and maintain. Moreover, these systems tend to be complicated and typically demand the services of a skilled and specialized work force to ensure they are adequately maintained.
The provision of an improved control system which can actively monitor the composition of gases in a container and provide an optimal environment for the storage of container contents would be of advantage.
The provision of a system able to effectively control the flow of gases into and/or out of a container to thereby promote a gaseous atmosphere in a container which will prolong the shelf life of stored produce would be of advantage. The provision of such a system which is both relatively inexpensive to produce and maintain would be advantageous.
An apparatus for controlling the atmosphere in a container is disclosed in International Patent Application No. WO 2004/107868 disclosing a container including a plurality of walls and at least one inlet and/or outlet. Within the container is an apparatus including a sensor, a controller and a gas permeable membrane being adapted to facilitate the passage there through of different gases at different rates. The membrane separates the container into a first region and a second region, the first region being for holding cargo, and the second region defining a gas buffer region, where at least one inlet and/or outlet communicate(s) with the buffer region.
A problem to be solved is to achieve a controlled atmosphere in the cargo region of a container, wherein a membrane is able to obtain and hold low concentrations of carbon dioxide and of oxygen in the atmosphere in the cargo region. It may be disadvantageous if it is necessary to design a specific membrane to use with each kind of perishable goods, such as fruit and/or vegetables.